1. Field of the Invention
The present invention relates to a sound reproducing apparatus and a sound reproducing method and, more particularly, to a sound reproducing apparatus employing a head related transfer function (HRTF) to generate a virtual source and a sound reproducing method using the same.
2. Description of the Related Art
In the audio industry of the related art, output sounds were formed on a one-dimensional front or two-dimensional plane to generate substantial sounds close to vivid realism. In recent years, most sound reproducing apparatus have thus reproduced stereo sound signals from mono sound signals. However, the presence range which may be detected by sound signals generated when the stereo sound signals are reproduced was limited depending on a position of a speaker. To cope with this limit, research was conducted on an improvement of speaker reproduction capability and reproduction of virtual signals by means of signal processing in order to extend the present range.
As a result of such research, there exists a representative surround stereophonic system which uses five speakers. It separately processes virtual signals output from a rear speaker. A method of forming such virtual signals includes having a delay in response to a spatial movement of the signal and reducing the signal size to deliver it to the rear direction. To deal with this, most of the current sound reproducing apparatuses employ a stereophonic technique referred to as DOLBY PROLOGIC SURROUND, so that vivid sounds having the same level as the movie may be experienced even at home.
As such, vivid sounds close to presence may be obtained when the number of channels increases, however, it requires the number of speakers to be additionally increased by the increased number of channels, which causes cost and installation space to be increased.
Such problems may be improved by applying research results about how humans hear and recognize sounds in a three-dimensional space. In particular, much research has been conducted on how humans can recognize the three-dimensional sound space in recent years, which generates virtual sources to be employed in an application field thereof.
When such a virtual source concept is employed in the sound reproducing apparatus, that is, when sound sources in several directions may be provided using a predetermined number of speakers, for example, two speakers instead of using several speakers in order to reproduce the stereo sound, the sound reproducing apparatus is provided with significant advantages. First, there is an economical advantage by using a reduced number of speakers, and second, there is an advantage of a reduced space occupied by the system.
As such, when the conventional sound reproducing apparatus is employed to localize the virtual source, a HRTF measured in an anechoic chamber or a modified HRTF was used. However, when such a conventional sound reproducing apparatus is employed, a stereophonic effect which has been reflected at the time of recording is removed, so that listeners hear the sound which is not an initially optimized sound but a distorted one. As a result, sounds required by the listeners were not properly provided. To solve this problem, a room transfer function (RTF) measured in an optimal listening space is used instead of the HRTF measured in an anechoic chamber. However, the RTF used for correcting the sound requires a large number of data to be processed as compared to the HRTF. As a result, a separate high performance processor capable of operating main factors within a circuit in real time, and a memory having a relatively high capacity are required.
In addition, existing reproduced sounds, which were intended to have features of the optimal listening space and the sound reproducing apparatus at the time of recording, become actually distorted depending on the listening space and speakers used by listeners.